{-# LANGUAGE Arrows #-}
-- | This module defines the game as a big Signal Function that transforms a
-- Signal carrying a Input 'Controller' information into a Signal carrying
-- 'GameState'.
--
-- There is no randomness in the game, the only input is the user's.
-- 'Controller' is an abstract representation of a basic input device with
-- position information and a /fire/ button.
--
-- The output is defined in 'GameState', and consists of basic information
-- (points, current level, etc.) and a universe of objects.
--
-- Objects are represented as Signal Functions as well ('ObjectSF'). This
-- allows them to react to user input and change with time.  Each object is
-- responsible for itself, but it cannot affect others: objects can watch
-- others, depend on others and react to them, but they cannot /send a
-- message/ or eliminate other objects. However, if you would like to
-- dynamically introduce new elements in the game (for instance, falling
-- powerups that the player must collect before they hit the ground) then it
-- might be a good idea to allow objects not only to /kill themselves/ but
-- also to spawn new object.
--
-- This module contains two sections:
--
--   - A collection of gameplay SFs, which control the core game loop, carry
--   out collision detection, , etc.
--
--   - One SF per game object. These define the elements in the game universe,
--   which can observe other elements, depend on user input, on previous
--   collisions, etc.
--
-- You may want to read the basic definition of 'GameState', 'Controller' and
-- 'ObjectSF' before you attempt to go through this module.
--
module Objects.Walls where

-- External imports
import Prelude hiding (id, (.))
import Control.Category (id, (.))
import Data.List
import Data.Maybe
import Debug.Trace
import FRP.Yampa
import FRP.Yampa.Extra
import FRP.Yampa.Switches

-- General-purpose internal imports
import Data.Extra.Ord
import Data.Extra.VectorSpace
import Physics.Oscillator
import Physics.TwoDimensions.Collisions       as Collisions
import Physics.TwoDimensions.Dimensions
import Physics.TwoDimensions.GameCollisions
import Physics.TwoDimensions.Shapes
import Physics.TwoDimensions.PhysicalObjects

-- Internal iports
import Constants
import GameState
import Input
import Objects
import ObjectSF

-- * Walls

-- | Walls. Each wall has a side and a position.
--
-- NOTE: They are considered game objects instead of having special treatment.
-- The function that turns walls into 'Shape's for collision detection
-- determines how big they really are. In particular, this has implications in
-- ball-through-paper effects (ball going through objects, potentially never
-- coming back), which can be seen if the FPS suddently drops due to CPU load
-- (for instance, if a really major Garbage Collection kicks in.  One potential
-- optimisation is to trigger these with every SF iteration or every rendering,
-- to decrease the workload and thus the likelyhood of BTP effects.
objSideRight  :: ObjectSF
objSideRight  = objWall "rightWall"  RightSide  (gameWidth, 0)

-- | See 'objSideRight'.
objSideLeft   :: ObjectSF
objSideLeft   = objWall "leftWall"   LeftSide   (0, 0)

-- | See 'objSideRight'.
objSideTop    :: ObjectSF
objSideTop    = objWall "topWall"    TopSide    (0, 0)

-- | See 'objSideRight'.
objSideBottom :: ObjectSF
objSideBottom = objWall "bottomWall" BottomSide (0, gameHeight)

-- | Generic wall builder, given a name, a side and its base
-- position.
objWall :: ObjectName -> Side -> Pos2D -> ObjectSF
objWall name side pos = arr $ \(ObjectInput ci cs) ->
  Object { objectName           = name
         , objectKind           = Side side
         , objectPos            = pos
         , objectVel            = (0,0)
         , canCauseCollisions   = False
         , collisionEnergy      = 0
         }